Rotary mowers currently predominate over other types such as reel mowers, particularly in the home-owner field for mowing lawns. A rotary mower conventionally comprises a housing in which a rotor is mounted for rotation about a generally vertical axis. The rotor has outer cutting edges traveling in a generally horizontal plane although sometimes the cutting plane may be slightly tilted downwardly toward the front of the mower with a corresponding tilt of the vertical axis. Such tilts are included herein within the horizontal and vertical terminology. Also the terms are with respect to ground, since both level and sloping surfaces may be mowed.
The housing of a rotary mower conventionally has a deck with a skirt which extends downwardly to approximately the height of the blade cutting plane and the entire area swept by the blade is generally open to the ground surface. A gasoline or electric motor is mounted on the deck, with a vertical shaft to which the rotor is attached. In tractor units, power take off may be provided from the tractor motor.
Cutting by rotary mowers is accomplished by the high speed impact of the cutting blades on the grass. In the past, tip velocities exceeding 20,000 feed (6100 meters) per minute have been employed. Such mowers have been recognized to be highly dangerous to the feet (or hands) of a user, and to nearby persons since stones, etc. may be thrown with great velocity. Nevertheless, the relative simplicity and lower cost as compared to reel and other types of mowers, the greater ease of sharpening, and the ability to cut tall as well as short grass, has resulted in wide-spread use of the rotary mower.
In recent years, efforts to reduce rotary mower dangers have included: lower blade tip speeds, trailing shields, discharge chute shields, safety interlocks, and blade guards. These safety features however have in many instances reduced the efficiency of the mower. For example lower tip speeds generally result in poorer cutting performance and increased plugging. Trailing shields provide some protection to the operator but particularly when high grass is being mowed are often a nuisance. Shields over the discharge chute reduce the danger of thrown debris but often increase plugging. The result is that safety features are some times bypassed or made ineffective by the operator in an attempt to improve mower performance or remove a nuisance.
A cross flow mower of the rotary type such as disclosed in U.S. application Ser. No. 970,197 provides a mower which has all of the advantages of a rotary mower but because it utilizes a cross flow principal, allows it to be combined with structure, such as a protective lower wall positioned between the ground and a large part of the path swept by the rotor blades, which overcomes the dangers associated with conventional cross flow blowers as outlined above. The mower of that application employs radial expansion in the housing surrounding the rotor to form and stabilize a vortex which in turn induces a cross flow of air through the rotor path from an inlet region to an outlet region of the mower.
The rotors of cross flow blowers conventionally have large axial to radial dimensions such that air flows predominantly transverse to the rotor axis with the result that to date only radial expansion of the housing has been practical to create and stabilize the vortex inducing the cross flow. This is because air cannot flow axially with respect to rotors over long distances in any efficient manner.
A problem with cross flow blowers generally is that they are sensitive to changes in back pressure as may occur in a mower when the outlet becomes plugged or partially plugged by cuttings. Changes in back pressure tend to shift or move the vortex which in turn effects the performance of the blower.
It is therefore an object of my invention to provide for a cross flow rotary type mower which will include a means for stabilizing the position of the vortex thus improving the safety of the mower while at the same time preserving the excellent performance of such mowers in handling of clippings without plugging.
It is a further object of the invention to provide for a mower construction which will use an axial expansion of a portion of the housing to stabilize the vortex to insure effective cross flow blower action notwithstanding changes in back pressure.